全文获取类型
收费全文 | 7087篇 |
免费 | 305篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 56篇 |
综合类 | 4篇 |
化学工业 | 1122篇 |
金属工艺 | 64篇 |
机械仪表 | 79篇 |
建筑科学 | 160篇 |
矿业工程 | 18篇 |
能源动力 | 177篇 |
轻工业 | 793篇 |
水利工程 | 24篇 |
石油天然气 | 18篇 |
无线电 | 214篇 |
一般工业技术 | 721篇 |
冶金工业 | 2933篇 |
原子能技术 | 21篇 |
自动化技术 | 990篇 |
出版年
2024年 | 10篇 |
2023年 | 44篇 |
2022年 | 156篇 |
2021年 | 199篇 |
2020年 | 124篇 |
2019年 | 147篇 |
2018年 | 187篇 |
2017年 | 176篇 |
2016年 | 179篇 |
2015年 | 154篇 |
2014年 | 193篇 |
2013年 | 340篇 |
2012年 | 330篇 |
2011年 | 362篇 |
2010年 | 283篇 |
2009年 | 240篇 |
2008年 | 254篇 |
2007年 | 212篇 |
2006年 | 164篇 |
2005年 | 147篇 |
2004年 | 106篇 |
2003年 | 98篇 |
2002年 | 93篇 |
2001年 | 44篇 |
2000年 | 41篇 |
1999年 | 114篇 |
1998年 | 842篇 |
1997年 | 466篇 |
1996年 | 330篇 |
1995年 | 208篇 |
1994年 | 168篇 |
1993年 | 185篇 |
1992年 | 28篇 |
1991年 | 51篇 |
1990年 | 47篇 |
1989年 | 50篇 |
1988年 | 52篇 |
1987年 | 45篇 |
1986年 | 32篇 |
1985年 | 39篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 18篇 |
1981年 | 17篇 |
1980年 | 34篇 |
1979年 | 7篇 |
1978年 | 12篇 |
1977年 | 99篇 |
1976年 | 216篇 |
1975年 | 13篇 |
排序方式: 共有7394条查询结果,搜索用时 15 毫秒
41.
JE Eberhart-Phillips PD Frederick RC Baron L Mascola 《Canadian Metallurgical Quarterly》1993,82(5):797-801
OBJECTIVE: To describe the effects of measles in pregnancy using a large case series. METHODS: Pregnant women with measles were identified by county health department records, and their hospital and clinic records were reviewed. When available, records for the infants of case patients were also reviewed. RESULTS: Fifty-eight pregnant women with measles were identified. Thirty-five (60%) were hospitalized for measles, 15 (26%) were diagnosed with pneumonia, and two (3%) died of measles complications. Excluding three induced abortions, 18 pregnancies (31%) ended prematurely; five were spontaneous abortions and 13 were preterm deliveries. All but two of the 18 pregnancies that terminated early did so within 14 days of rash onset. Two term infants were born with minor congenital anomalies, but their mothers had measles late in the third trimester. No newborns were diagnosed with congenital measles. CONCLUSIONS: The incidence of death and other complications from measles during pregnancy may be higher than expected for age-comparable, nonpregnant women. Measles in pregnancy may lead to high rates of fetal loss and prematurity, especially in the first 2 weeks after the onset of rash. 相似文献
42.
BACKGROUND: FRTL-5 thyroid cells are a cell line extensively used for the investigation of thyroid functions. Activation of alpha-1 adrenergic receptors stimulates both arachidonic acid (AA) release and cytosolic Ca2+ increase in this cell line. Cytosolic Ca2+ and arachidonic acid are known to be important second messengers regulating a variety of thyroid functions. The generation of these messengers is regulated primarily by two different types of phospholipases, phospholipase C (PLC) and phospholipase A2 (PLA2). METHODS: Norepinephrine (NE, 10 mumol/L) was used as an alpha-1 adrenergic activator, and cytosolic-free Ca2+ concentration ([Ca2+]i) was determined using the fluorescent dye indo-1. Arachidonic acid release was measured as an indicator of PLA2 activation, and protein kinase C (PKC) activity determination and isoforms identification were performed using commercial kits. RESULTS: Norepinephrine increased [Ca2+]i and AA release. Prevention of NE-induced cytosolic Ca2+ influx, either by removal of extracellular Ca2+ or by use of Ca2+ channel blockers, NiCl2 or CoCl2, inhibited AA generation entirely. Inhibition of NE-induced increase in [Ca2+]i by the Ca2+ chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), also significantly suppressed NE-induced AA release. Inhibition of PKC activity by PKC inhibitors (H-7 or staurosporine) or downregulation induced by prolonged treatment with phorbol 12-myristate 13-acetate (PMA) or thyleametoxin (TX) significantly blocked the NE-induced AA release, which indicates PKC is involved in mediating NE-induced AA release. Protein kinase C activity measurement indicated that NE induced an activation of PKC in 5 minutes. To further characterize the role of PKC or Ca2+ in regulation of AA release, we identified PKC isoforms by immunoblotting with specific antibodies against 8 different Protein kinase C isoforms. PKC-alpha, -beta I, -beta II, -gamma, delta, -epsilon, -zeta, and -eta isoforms were identified. Norepinephrine induced translocation of PKC-alpha, -beta I, -beta II, -gamma, -delta, and -epsilon isoforms but not -zeta and -eta from cytosol to membrane. Chelation of intracellular Ca2+, prevention of Ca2+ influx, or prolonged treatment with thymeleatoxin (TX) completely blocked the NE-induced translocation of PKC-alpha. CONCLUSIONS: These results, taken together with data obtained from AA experiments, suggest that PKC plays a critical role in alpha-1 adrenergic receptor mediated PLA2 activation and subsequent AA release. Extracellular Ca2+ influx is a prerequisite for both PKC-alpha translocation and AA release. Whether Ca2+ acts directly upon the PLA2, or via PKC-alpha, to regulate AA generation is an intriguing question that remains to be clarified. 相似文献
43.
44.
45.
46.
47.
Antonio J. Pérez-López José Manuel López-Nicolás Angel A. Carbonell-Barrachina 《European Food Research and Technology》2007,225(2):255-260
Consumers demand organic products because they believe that the organic products are more flavorful and respectful to the
environment and human health. The effects of organic farming on the minerals contents and aroma composition of Clemenules
mandarin juices were studied. Minerals (Fe, Cu, Mn, Zn, Ca, Mg, K, and Na) were quantified using atomic absorption-emission
spectroscopy, while volatile compounds were extracted using the dynamic headspace technique and were identified and quantified
by GC–MS. In general, organic farming produced a mandarin juice with a higher quality than that produced by conventional agricultural
practices. Higher concentrations of both minerals and positive volatile compounds were found in the organic juice, while the
formation of off-flavors was higher in the conventional juice, although threshold values were not reached. 相似文献
48.
The effects of cooking temperature, time and temperature of brine-salting, and temperature of ripening on the behavior of Enterobacteriaceae in Manchego cheese were studied. Fifty lots of cheese from raw ewe's milk manufactured and ripened under different conditions were investigated throughout a 60-day ripening period. Differences in pH values due to temperature-dependent whey retention accounted for the effect of cooking temperature on coliform and fecal coliform counts. Temperature of brine-salting had no effect on Enterobacteriaceae counts, but a significant effect of salting time on Enterobacteriaceae and fecal coliform counts was detected. Ripening temperature was the manufacturing variable with greatest influence (P<.01) on Enterobacteriaceae and coliform counts during the whole curing period. 相似文献
49.
50.
The treatment of patients with uterine neoplasms may be significantly altered by the stage of disease at the time of diagnosis. A noninvasive and accurate means of staging these tumors is therefore desirable. This article discusses the magnetic resonance imaging techniques and findings that are essential for the accurate staging of uterine neoplasms. The imaging findings are presented following a discussion of the histopathologic findings, clinical presentation, diagnosis and staging, pathways of tumor spread, and treatment of each neoplasm. A comparison of magnetic resonance and other imaging techniques is also provided. 相似文献